1. Field of the Invention
The present invention relates to a press roll for treating a material web in a nip. More particularly, the present invention relates to a press roll for treating material in a nip that has a press shoe which extends along the nip, a press jacket guided via the press shoe, and adjacent force elements (e.g., cylinder/piston units) disposed along an axis of the press roll and supported on a stationary carrier.
2. Description of Background Information
A prior art press roll of this type is shown, for example, in EP 0 345 501 B1. In this prior art press roll, the manufacturing costs are largely dependent on the desired uniformity of line force distributed laterally along the nip over the material web to be treated (typically a paper or cardboard web). If several individual force elements support the press shoe are with a spacing t therebetween along the direction of the roll axis, then a maximum deflection between the force elements is expressed by the equation: EQU f=c.multidot.P.sub.L .multidot.t.sup.4,
where c represents a constant related to the elastic resilience of the press shoe, P.sub.L represents the line force, and t represents the distance between adjacent force elements along the roll axis.
As can be seen from the above equation, minor variations in spacing t can significantly affect the uniform line force distribution, in that line force is reduced at points at which the press shoe sags. Excessive sag does not provide sufficient compression of the material web guided through the nip; indeed, the line force can drop to zero at the midpoint between force elements.
To eliminate sag points, the press roll shown in EP 0 345 501 B1 0uses two parallel rows of force elements that extend along the roll axis, lateral to the material web. Compared with a single row of force elements, the two-row design halves the distance between individual force elements while using the same total support area. While this reduces maximum deflection by reducing spacing t, it also increases the total number of force elements by a factor of four. However, not only are four smaller force elements more expensive than a single larger force element, the assembly of the larger number of force elements increases production time and associated costs. Further, the use of piston rods in the prior art force elements requires a significant amount of space in the radial direction to hold the force elements.